Since long time ago, there are two kinds of traditional manner to place integrated circuit package (abbreviated as IC package) on a circuit board (or called main board): one manner is directly welding wherein the IC package can not be pulled out, and another manner is replaceable wherein the IC package can be pulled out. The replaceable assembly device of an electrical connection device and a circuit board is usually adapted for IC package that needs upgrade or renew. And, when one of the circuit board or the IC package is out of order, another element still be remained for continuous usage. The assembly device of a socket and a circuit board for central processing unit (abbreviated as CPU) plugged in computer is a typical example.
Please refer to FIG. 1 and FIG. 2, which are illustrations for a replaceable assembly device typically seen in current market for assembling an IC package and its electric connector to a circuit board. In tradition, for the purposes of both replaceable and excellent connection, the common method is to arrange pins 111 on the IC package 11 and arrange electric connector 13 having plural pinholes on the circuit board 12 (or called main board) to place the IC package 11. Prior manners for packing IC package 11 are lead frame and ball grid array (abbreviated as BGA). Recently, for the IC package pursuing high performance (i.e., high heat dissipation) and high pin count, a flip chip BGA package is usually used. As shown in FIG. 1, its essential components are usually comprised of: an IC chip 112, which is arranged on one side surface of a substrate 113 by flip chip method; several solders, which are arranged on another side surface of the substrate 113, and which are electrically coupled to chip 112 by the circuit design of the substrate 113; and chip 112, another non-active surface of which is pasted with a heat sink 115. Since the pin 111 is not an object with extremely high rigidity, so it is easily twisted and damaged during the plugging and pulling procedures. The pin 111 is also uneasily connected to the solder 114 firmly so, according to the current techniques, plural pins 111 must be fixed on an interposer before being welded to the solder 114.
As regarding to be plugged through the pin 111 of the prior IC package 11 and have the replaceable function, the prior pin-type electric connector 13 currently used all includes following components: a socket 132, which has plural pinholes 131 and is welded on the circuit board 12; a sliding plate 133, which is arranged over the top face of the socket 132 by a linearly sliding manner; and a long pulling rod 134, which is arranged at one side of the socket 132 for driving the sliding plate 133 to proceed a slight slide. In each pinhole 131 of the socket 132, a holder 137 is arranged. And, there is a solder pad 135 formed at the bottom of the pinhole 131. The lower end of the holder 137 is extended out of the bottom of the pinhole 131 to form pin 1371 that will be plugged into the penetration hole 121 of the circuit board 12. A conducting layer 122 is arranged in the penetration hole 121 of the circuit board 12 for being electrically connected to the pin 1371. On the upper surface of the circuit board 122, solder mask 124 is used to define the penetration hole 121 and the contact pad 1221 thereon. The pin 1371 together with the socket 13 is welded fixedly upon the circuit board 12 by solder material 123, 125. A lightly larger opening (not shown in the figures) is arranged at the position corresponding to the pin 131 on the sliding plate 133. Pressing down the long pulling rod 134 will make it rotate around the rod axis 136 until it is horizontal to the socket 132, such that the sliding plate 133 proceeds a slightly sliding movement to fix the pin 111 of the IC package 11 into the pinhole 131. When the IC package 11 is going to be pulled out, then it is necessary to rotate the long pulling rod 134 to become 90 degrees vertically to the socket 132, such that the pin 111 will be loosened to take out the IC package 11.
Please refer to FIG. 3 and FIG. 4, which show another replaceable assembling device according to prior art for connecting an IC package and a socket to a circuit board. Since the structures of the IC package 11 and the electric connector 13a according to this prior art are substantially same as those of the prior art described in FIG. 1, so its assembling components and structures are not described in detail herein, but only an illustration drawn by broken lines shows its entire outer appearance of assembly. As shown in FIG. 3, the biggest difference between this electric connector 13a and the one described in aforementioned prior art is that the bottom of the electric connector 13a is not shown as pin-typed structure but uses several solder balls 138. And, the lower end of the holder 137a in the electric connector 13a is bent directly to 90 degrees to be acted as a pad 139 connected to the solder ball 138. Instead of arranging penetration hole, a solder pad 126 is arranged on the circuit board 12a. Making the solder ball 138 of the electric connector 13a and the solder pad 126 on the circuit board 12a proceed a corresponding hot welding process (the so-called solder pot or solder reflow process) will melt the solder ball 138 and weld it fixedly between two pads 139, 126. The shortcoming of this prior art is that: for both the pad 139 arranged at the lower end of the holder 137 of the electric connector 13a and the solder pad 126 arranged upon the circuit board 12a, they are all structures of simple plane, so the solder ball 138 is connected to the pads 139, 126 by plane contact. Therefore, the electric characteristic is relatively poor because of small contact surface, and the structural strength of connection is also relatively poor. So, the product yield is low, and the solder ball 138 even drops off. In the hot welding process, the material of solder ball 138 is overflowed to cause short circuit and electric unsteadiness. In the meantime, the co-planarity between the electric connector 13a and the circuit board 12a is often in poor condition after they are connected together.